Numerous methods and devices have been employed in the past for coating fasteners. Some of these methods and devices are useful in coating certain types of fasteners, but are not as versatile as may be necessary to coat other types of fasteners.
Examples of such methods and devices include U.S. Pat. No. 3,452,714 in the names of G. F. C. Burke, Richard J. Duffy et al., U.S. Pat. No. 4,120,993 to Richard J. Duffy et al., and U.S. Pat. No. Re. 28,812 to Richard J. Duffy, one of the present inventors. The methods and devices disclosed in these United States Patents provide for the coating of fasteners in which the shank portion of the fastener depends below a pair of traveling belts. The fasteners are supported on the belts at their head portion. These methods and apparatus prove very efficient for coating fasteners which are void of projections depending downwardly from the head portion of the fastener, since such fasteners may be positioned with the shanks between the belts and remain in a stable position for coating. However, these methods and apparatus prove somewhat inefficient and less versatile than required when fasteners including projections depending downwardly in the direction of the shank portion are to be coated as well as rotated during the coating process. Fasteners including such projections are not readily placed in a stable position with their shank portions projecting downward between the belts and can not be easily and efficiently coated in this configuration. Furthermore, the methods and apparatus of the previously described patents do not provide the ability to precisely control the linear speed and rotation of the fasteners during the coating process.
Thus, it would be advantageous to provide a method and apparatus which coated a large variety of fasteners, including fasteners having projections depending downwardly from the head portion of the fastener, in a cost efficient, versatile and continuous manner. Further, it would be advantageous to provide a method and apparatus which would automatically and rapidly coat a wide variety of fasteners, including those fasteners having projections depending downwardly from their head portion.
It would also be advantageous to provide a method and apparatus which accommodates a variety of fastener sizes and which could be quickly and easily adapted for coating various sizes of both male and female fasteners. In addition, it is desirable to provide a method and apparatus which has the versatility to coat a specified portion of the threads of the fastener, as well as the complete threaded area, and further, a method and apparatus which may coat only a specific portion of the radial distances about the threaded surface of the fastener. Furthermore, it would be advantageous to provide a method and apparatus which provides the ability to precisely control the linear speed and rotation of the fasteners to be processed in both a shank up as well as a shank down orientation.